Many different types of radio transmitters have been developed as shown in FIGS. 1A-1G. Conventional transmitters may be classified into either a constant envelop transmitter or a non-constant envelope transmitter, depending on the nature of the signal that the transmitter amplifies. The conventional transmitters shown in Figures 1A-1G employ analog and/or digital techniques to generate a signal.
FIG. 1A shows a conventional analog Cartesian modulation, direct conversion transmitter 110. The transmitter 110 may amplify both constant and non-constant envelope signals. The transmitter 110 employs an analog In-phase (I)/quadrature (Q) modulator. An efficient class B power amplifier may be used when amplifying a constant envelope signal and a class AB power amplifier may be employed when amplifying a non-constant envelope signal. I and Q components output by a modem 111 are converted to I and Q analog signals by digital-to-analog converters (DACs) 112. The I and Q analog signals are upconverted by mixers 113. The upconverted I and Q signals are combined and amplified by a variable gain amplifier (VGA) 114 and a power amplifier (PA) 115. Transmit power control (TPC) may be performed at the VGA 114. The amplified signal output by the PA 115 is filtered by a filter 116 and transmitted.
FIG. 1B shows a conventional constant envelope, analog polar modulation transmitter 120. Since the amplified signal is a constant envelope signal, only angle information is necessary in the polar representation of the signal. The angle information from a modem 121 is converted to an analog angle signal by a DAC 122. The analog angle signal is used to modulate a voltage controlled oscillator (VCO) 124 through a phase locked loop (PLL) 123. The modulated output of the VCO 124 is then amplified by a PA 125, (e.g., a class B PA). TPC may be implemented by varying the collector or drain voltage of the PA 125. The amplified signal output by the PA 125 is filtered by a filter 126 and transmitted.
FIG. 1C shows a conventional constant envelope, digital polar modulation transmitter 130. The angle information from a modem 131 is used to modulate a numerically controlled oscillator (NCO) 132. The multi-bit output of the NCO 132 is then fed to a TPC unit 133. The multi-bit output of the TPC unit 133 is then used to drive a high power DAC 134. The DAC 134 is used as a PA. The DAC reference voltage may be used to implement additional TPC functionality. The amplified signal output by the DAC 134 is filtered by a filter 135 and transmitted.
FIG. 1D shows a conventional non-constant envelope, analog polar modulation transmitter 140. This transmitter 140 is commonly known as an envelope elimination and restoration (EER) transmitter. Two signal paths are formed in the transmitter 140, a primary path and a supplementary path. An analog I/Q modulator is used in the primary path to form a signal which contains both the angle and magnitude information. I and Q components of the signal output by a modem 141 are converted to I and Q analog signals by DACs 142. The I and Q analog signals are upconverted by mixers 143. The upconverted I and Q signals are combined and passed through a limiter 144, where the magnitude information is eliminated. Only the angle information is retained at the output of the limiter 144. The output of the limiter 144 is then passed through a TPC unit 145 and fed into a PA 146, (e.g., a class AB PA).
The magnitude information of the signal is carried through a supplementary path. The I and Q components are fed into an envelope detector 147. The output of the envelope detector 147 retains only the magnitude information of the signal. The magnitude information is then converted to an analog form by a DAC 148 and combined with the angle information at the PA 146, (i.e., PA collector or drain). The combined signal is filtered by a filter 149 and transmitted.
FIG. 1E shows a conventional non-constant envelope, analog polar modulation transmitter 150. The angle information from a modem 151 is converted to an analog signal by a DAC 152a to modulate a VCO 154 through a PLL 153. The modulated VCO output is then passed through a TPC unit 155. The output of the TPC unit 155 drives a PA 156, (e.g., a class AB PA). The magnitude information from the modem 151 is converted to an analog form by a DAC 152b and combined with the angle information at the PA 156, (i.e., PA collector or drain). The combined signal is filtered by a filter 157 and transmitted.
FIG. 1F shows a conventional non-constant envelope, digital Cartesian modulation transmitter 160. A modem 161 outputs I and Q components of a signal. The I and Q components may be attenuated by multipliers 162 for TPC functionality. A 4-to-1 multiplexer 163 is used as an I/Q modulator. Both the true and the inverted forms of the I and Q components are input into the multiplexer 163. The multiplexer 163 sequentially passes one of the four input signals to the output in such a manner that a repeating pattern of I, Q, −I, −Q (or other sequences) results at the output. The multi-bit output of the multiplexer 163 is then converted to an analog form by a DAC 164. The DAC 164 is used as a PA. The DAC reference voltage may be used to implement additional TPC functionality. The amplified signal is filtered by a filter 165 and transmitted. U.S. Pat. No. 5,101,418 also discloses a transmitter including a digital quadrature frequency upconverter.
FIG. 1G shows a conventional non-constant envelope, digital polar modulation transmitter 170. The angle information from a modem 171 is used to modulate an NCO 173. The multi-bit output of the NCO 173 is then fed through a TPC unit 174. The multi-bit output of the TPC unit 174 is then used to drive a high power DAC 175. The magnitude information from the modem 171 is converted to an analog form by a DAC 172 and combined with the angle information at the DAC 175, (i.e., DAC reference voltage input). The DAC 175 is used as a PA. The amplified signal is filtered by a filter 176 and transmitted.
Conventional transmitters such as those disclosed hereinbefore deliver lower than desired power efficiency for on-constant envelope signals. Conventional transmitters often utilize analog circuit technology where repeatable performance is costly to achieve. Analog circuit technology-based conventional transmitters have low noise immunity compared to digital circuitry and therefore are difficult to integrate with a modem chip.